1. Technical Field
The invention relates generally to the field of firearms and is directed to an improved method of manufacture for wooden gunstocks for use with firearms. More specifically, the invention is directed to an improved method for manufacturing wooden gunstocks from heat treated wood to achieve desirable characteristics for the gunstocks while preserving the aesthetics of natural wood.
2. Description of Prior Art
A gunstock is a part of a firearm that is primarily held by the shooter. It has a rear portion, known as the butt, which generally is rested against the body of the shooter to stabilize the firearm, and a forward portion, known as the fore-end, which attaches to the firing mechanism of the firearm. Firearms manufacturers have historically manufactured gunstocks from wood. Wooden gunstocks are aesthetically unique and naturally beautiful, but they have some characteristics that are difficult for firearm manufacturers to work with. Wooden gunstocks take up and give off moisture depending on the climate and varying weather conditions, resulting in shrinkage and expansion. This shrinking and expansion of a gunstock, however slight, can affect the accuracy of the firearm. Also, some wood that would be otherwise desirable for use in gunstocks, because of hardness, aesthetics, or other characteristics, are too dense, making them too heavy for firearm manufacturing.
As a result of these shortcomings, firearms manufacturers have recently opted for synthetic materials for gunstocks, since synthetic gunstocks offer a lighter gunstock than wood, are more resistant to moisture and rot, and tend to have greater strength than wooden gunstocks. Nevertheless, wooden gunstocks are still desirable, for their aesthetics and tactile qualities, as well as historical fidelity, and therefore a method of manufacture of wooden gunstocks that overcomes the deficiencies of traditional wooden gunstocks is desired.
One method for decreasing the susceptibility of wooden gunstocks to moisture and rot is to chemically treat the wood before fashioning it into a gunstock. A common method of chemically treating wood is the “pressure treatment” method, in which the wood is treated with chemicals such as arsenic and chromium (Chromate Copper Arsenate), alkaline copper quaternary (ACQ), or copper azole preservative, applied to the wood using a vacuum and pressure cycle to force the chemicals deep into the inner portions of the wood. Other chemicals may also be used. While this method tends to improve the weather resistance as well as insect and rot resistance of the wood, it does not address swelling and shrinkage issues. The toxicity of the chemicals used also renders this method less than desirable.
Another method for decreasing the susceptibility of wooden gunstocks to moisture and rot is to treat the wood in a non-pressurized manner with preservatives. These preservatives may be chemically based or derived from naturally occurring compounds, such as oils, and the preservatives are applied to the surface of the wood. While this method tends to be simpler than the pressure treatment method, and potentially uses less toxic preservatives, it fails to ensure a uniform application of the preservative into the inner portions of the wood. It also does not address swelling and shrinkage issues.
There is known in the art yet another method for decreasing the susceptibility of wooden gunstocks to moisture and rot, which is preferable to the above-described methods. Wood may be heat treated prior to being fashioned into a gunstock. European Patent Application EP 0 922 918 A1 (Aug. 3, 1998), to Lallukka, Tero, for “Method for heat treatment of timber”, discloses such a method for treating wood.
Wood is made up, generally, of cellulose, lignin, and extractives. Cellulose (and hemicelluloses) are carbohydrates that are structural components in wood. Cellulose constitutes 40-50% and hemicelluloses 25-35% of wood. The composition and contents of hemicelluloses vary from one wood species to another. During heat treatment, both groups undergo changes, but the majority of the changes occur in hemicelluloses. After heat treatment, the wood contains a substantially lower amount of hemicelluloses. As a result of this, the amount of fungi susceptible material is significantly lower, providing one reason for heat-treated woods improved resistance to fungal decay compared with normal kiln dried wood. With the degrading of the hemicelluloses, the concentration of water-absorbing components decreases and the dimensional stability of treated wood is also improved compared to normal kiln dried wood. The decomposition temperature of the hemicelluloses is about 200-260° C., and the corresponding temperature for cellulose is about 240-350° C. Lignin holds the wood cells together. Lignin constitutes 20-30% of wood. During heat treatment, bonds between components of lignin are partially broken. Of all wood's constituents, lignin has the best ability to withstand heat. Lignin's mass starts to decrease when the temperature exceeds 200° C. Wood also contains minor amounts of small-molecule constituents known as extractives. Extractives constitute less than 5% of wood. Extractives are not structural components in wood, and most of the compounds evaporate easily during the heat treatment.
Heat treating wood changes the structure of the wood in a manner which is desirable for the manufacture of gunstocks. During heat treatment, wood undergoes mild pyrolysis, resulting in degradation of hemicelluloses and amorphous cellulose, modification of lignin structures, and evaporation of extractives from the wood. The lignin and hemicelluloses become less hygroscopic. Surface hardness increases, moisture is 10%-50% less than in untreated wood, resins dry out or evaporate, less absorption of moisture occurs, as well as reduced molding, improved weather resistance, and moisture deformation is reduced by 30% to 90% over untreated wood.
Thermally modified wood has a lower density than untreated wood. This is mainly due to the changes of the mass during the treatment when wood loses its weight. Density decreases as higher treatment temperatures are used. This leads to overall lighter weight of the wood, a desirable characteristic for gunstocks. However, the strength of wood has a strong correlation with density. Because thermally modified wood has slightly lower density after the treatment, it is somewhat less strong than untreated wood. However, the change in the weight-to-strength ratio is minimal. The strength of wood is also highly dependent on the moisture content and its relative level below the grain saturation point. Thermally modified wood benefits due to its lower equilibrium moisture content. Heat treated wood is therefore sufficiently strong for use in gunstocks.
Heat treatment also significantly reduces the tangential and radial swelling of wood. Heat-treated wood consequently has very low shrinkage. The water permeability of heat-treated wood is 20-30 percent lower than that of normal kiln dried wood. Thermally modified wood is resistant to insects (which are attracted to the extractives of untreated wood; such extractives are largely evaporated away during heat treatment).
In summary, heat treating wood reduces its moisture content; it reduces the ability of the wood to absorb environmental moisture; it increases the surface hardness of the wood; it increases the overall stability of the wood (that is, minimizes expansion and shrinkage); it causes the wood to become less dense, and therefore lighter; and it makes the wood less susceptible to rot and insect predation. Heat treatment of wood further accomplishes these desirable characteristics without the use of toxic chemicals.
From the foregoing it is evident that there is a need for an improved method of manufacture for wooden gunstocks.
It is therefore an objective of the present invention to provide an improved method of manufacture for wooden gunstocks using heat treated wood.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks applicable to various species of wood.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks that reduces the moisture content of the wooden gunstock to minimize expansion and shrinkage and to increase the stability thereof.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks that makes the wood less susceptible to environmental moisture.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks that makes the wood less susceptible to rot and insect predation.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks that decreases the density and therefore the weight of the wood.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks that increases the surface hardness of the wood.
It is a further objective of the present invention to provide an improved method of manufacture for wooden gunstocks which does not use toxic chemicals to treat the wood.
Other objectives of the present invention will be readily apparent from the description that follows.